Discussion on: You don't need Array.reduce()

[JavaScript Joel]

for loops either mutate data or perform side effects, which as a general rule why they are good to avoid.

map, filter, and reduce also allow better code reuse and testability because it can be broken down further than a for loop can.

Example:

// modular, reusable, testable!
const add = (a, b) => a + b

// readable!
const sum = array.reduce(add)

You'll also notice all those lets go away and become const.

Get rid of for loops and it's possible to write your entire program without a single var or let!

[crazy4groovy]

I think you mean

const add = (a, b) => a + b
const sum = array.reduce(add, 0)

You need a seed value.

[JavaScript Joel]

Nope. That is exactly what I meant.

The seed is optional. If you don't provide a seed, the first item in the array is given as the accumulator.

Run the code!

const add = (a, b) => a + b

[1, 2, 3].reduce(add) //=> 6

[Fregante]

Sum is just about the only case where reduce is useful, but in reality it should never be passed around like that. Why keep an add function around that is only meant to be used together with a reduce? Just wrap it once and never use reduce again:

const sum = (array) => array.reduce((a, b) => a + b);

sum([1, 2, 3]) //=> 6

Don't tell me arr.reduce(add) makes more sense than sum(arr) because it doesn't.

In reality you can write sum event more efficiently with a regular loop and every part of your code benefits.

[Average Joe]

But if you don't pass any initial value then there would be errors in case of empty arrays. Example: